FPGA firmware YQ090421:

- implemented better keyboard interrupt handling (compatibility - Citadel)
- rewritten CPU interface (compatibility - faster write cycles)
- 28 MHz CPU turbo mode (new feature)
- rewritten SRAM interface - now compatible with most ISSI SRAMs
- memory support up to 3.5 MB (requires extra SRAM chips)
- flexible memory bank assignment
- implemented Amiga-like memory bus sharing between CPU and Blitter (compatibility)
- implemented fast Blitter mode (new feature)
- rewritten DMA slot allocation (compatibility)
- improved copper FSM (compatibility)
- double speed floppy disk dma mode (new feature)
- support for up to 4 (ARM) or 2 (PIC) floppy drives (new feature)
- implemented A1200/A600 IDE hard disk interface (requires ARM MCU) (new feature)
- rewritten audio DMA engine (compatibility)
- rewritten beam counters (compatibility)
- composite sync generation for S-Video/Composite video encoder (Minimig-ITX)
- rewritten display dma engine (compatibility)
- changed horizontal scroll value calculation (compatibility)
- implemented undocumented BPLCON2 feature (compatibility - Swiv)
- fixed collision detection (compatibility - Menace)
- rewritten breakpoint triggering in Action Reply (compatible with CPU turbo mode)
- implemented scanline emulation in scandouble mode (new feature)
- changed transparency level of OSD menu
- implemented full keyboard support in OSD menu (new feature)
- OSD joystick glitch filtering
- selectable PAL/NTSC mode (new feature)
